Code Manual for CONTAIN 2.0 - Federation of American Scientists

default correlations with ones of the same form but with larger coet%cients. The second is to use the
HMXMUL keyword discussed in Section 10.1.3.5 for applying a multiplier to the Nusselt number ~
that would otherwise be used at a gas-structure interface. Since a heat and mass transfer analogy is
used in CONTAIN to obtain the Sherwood number N~~from the Nusselt number N~u,any change
in N~uwill also affect N~~.In this case the ratio of heat to mass transfer would not be altered.
The third method is to use the keyword RMX2HX for specifying a multiplier by which N~~is
increased (or decreased) from the value obtained from N~Uthrough the heat and mass transfer
analogy. This multiplier does not affect N~U.This input option is the only option that will directly
alter the ratio of heat to mass transfer, besides omitting the CONDENSE keyword for a cell, which
will result in no condensation at all in that cell. In all other cases, this ratio will be determined by
the mass and heat transfer analogy.
10.2.2 Condensate Films on Heat Transfer Structures
The total mass in the water film on a heat transfer structure is required for a) the evaluation of total
heat transfer to a surface, and b) to determine the reservoir of water on structures that is available
for evaporation. The amount of water in the film is modeled in one of two ways. In the default
modeling, a film is allowed to accumulate but not permitted to flow if the film thickness 6 is less
than “mndpth,” the fixed minimum depth for the surface at which flow is allowed. However, the
film is permitted to flow as necessary to maintain this depth. This depth maybe specified by the user
as “mndpth” in the heat transfer structure input block described in Section 14.3.1.3. The default for
“rnndpth” in this default film treatment is 0.0005 m.
The second approach uses one-dimensional steady-state film flow correlations for either laminar or
wavy larninar film flow, assuming no shear at the gas-film interface. This approach, which is
applicable to the inner surfaces of structures, is referred to as the film tracking model, and is
activated by the FILMFLOW input in the BCINNER input block of the structure input, as discussed
in Section 14.3.1.3. Provisions have been made within the film tracking model to allow film
behavior to be modeled over a generalized surface represented by a number of structure inner
surfaces.
To better picture what is involved with this model, a number of structure inner surfaces are shown
in Figure 10-6. This figure shows how these surfaces maybe combined in a way that allows the
simulation of film flow over a more general surface. Each surface is considered a “node” for the
purpose of defining the flow characteristics of the surface. The mass conservation equation for the
film is applied to each “half-node” of a surface, defined by a horizontal line that splits the inner
surface into two equal areas. The correlations defined below are assumed to relate the average depth
8 and average velocity v~of the film along this line, and these quantities then define the mass flow
rate from the upper half-node to lower half-node and the film runoff rate from the structure. The
user may specify the node width w along the equal-area line and the angle of inclination (3at this line.
By default, these are determined by the structure type and orientation. As shown in Figure 10-6, a
fraction of the film runoff from thejth structure maybe allocated to the ith structure through the film
transfer matrix Sji, which is specified by the user through the DIVERT keyword. Thus, twodimensional
quasi-steady-state film flow down a series of structures can be simulated.
Rev O 10-28 6/30/97